Process for forming an integral hinged single wall blow molded container

ABSTRACT

An integral hinged blow molded container having a single wall is produced by inflating a parison within a mold having a hinge forming area with a draw ratio of greater than 1 whereby the parison is reduced in thickness within the hinge forming area relative to the adjacent area. The thus formed parison is severed about a circumference adjacent the formed hinge to create a top portion and a bottom portion openable and closable about the hinge.

This is a division of application Ser. No. 133,778, filed Mar. 26, 1980,now abandoned.

BACKGROUND OF THE INVENTION

This invention relates generally to the art of blow molded containersand the molding thereof and more particularly to the art of forming asingle-walled blow molded container having an integral hinge portion.

Single-walled thermoplastic containers have been produced in the priorart by utilizing injection molding techniques. Molds for injectionmolding processes are considerably more expensive and complex than moldsutilized for blow molding since a mold surface is required for everysurface of the resulting injection molded article. An example of suchprior art injectionmolding is described in U.S. Pat. No. 2,687,157 toCowan.

U.S. Pat. No. 3,795,265 to Schurman et al describes a process ofproducing a double-walled container having an integral hinge. In anaspect of the invention disclosed therein, there is provided a containerhaving a body part and a cover part joined by a hinge continuous witheach of them and connecting them for opening and closing the container.The body part, cover part and hinge are formed from a single plastictubular member. The hinge is a pressed and fused laminate of two websformed from opposite sides of the tubular member. The hinge is thinnerthan the adjacent wall area of the body part and the cover part, as aresult of the pressing and the pinching of the hinge during itsformation.

The method described by Schurman et al involves the use of anunrestrained parison and a mold having male mold parts that make asubstantial entry into the mating female mold parts. The method includesextruding the parison, positioning the unrestrained parison in the mold,closing the mold on the parison until the male mold parts projectsubstantially into the mating female mold parts deforming the parisonbetween them into the general configuration of the finished molded partsand inserting a blow needle through the wall of the parison andexpanding the parison by providing a pressured differential between theinvention and the outside of the parison by blowing a pressurized fluidinto the interior of the parison thus forcing the parison into thedetailed configuration of the closed mold.

The two mold cavities are joined by land surfaces that register inclosely spaced opposed relation when the mold is closed. The parison isclosed at opposite ends and pinched upon itself intermediate its ends,upon the closing of the mold, and compression molded at its intermediatepinched area between the land surfaces to form a hinge separating theparison into a pair of hollow compartments.

While the product described in the above referenced United States patentprovides an excellent double-walled container with an integral hinge, itis not always necessary for a container to have the double-wallconstruction described therein.

SUMMARY OF THE INVENTION

It is thus an object of this invention to provide a single-walled blowmolded container having a top portion and a bottom portion connected byan integral hinge portion.

It is a further object of this invention to provide a blow moldingprocess for producing a single-wall blow molded container with top andbottom portions connected by an integral hinge portion.

It is a further object of this invention to provide a process ofproducing a single-walled blow molded container having an integral hingeformed during the process of blow molding.

It is a further and more particular objective this invention to providea blow molding apparatus having the capability of forming a hingeportion during the blow molding process.

These as well as other objects are accomplished by inflating a parisonwithin a mold having a hinge forming area with a geometry to create adraw ratio of greater than 1 to 1 whereby the parison is reduced inthickness within the hinge area as compared to the area immediatelyadjacent the hinge area. The parison is severed along the circumferencecoincidental with the hinge area to form top and bottom sectionsconnected by the hinge section.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an isometric view of a container in accordance with thisinvention in the closed position.

FIG. 2 is an isometric view of the container of FIG. 1 in a partiallyopen position.

FIG. 3 is a section view of a blow mold in accordance with thisinvention.

FIG. 4 is a view of the blow mold of FIG. 3 in the closed position.

FIG. 5 is a view along the line 5--5 of FIG. 4.

FIG. 6 is a blow up of the hinge forming section of a mold in accordancewith this invention.

DETAILED DESCRIPTION

In accordance with this invention, it has been found that asingle-walled blow molded container having an integral hinge may beformed by deep drawing a hinge portion during the blow molding process.The molded parison with the deep drawn hinge portion is severed along acircumference contiguous with the hinge portion whereby the container isopenable and closable about the hinge area. Further and more particulardescription will be given with reference to the various figures ofdrawing.

A container 1, in accordance with this invention, is shown in anisometric view within FIG. 1 of the drawing. The container comprises abottom section 3, a top section 5 and a hinge portion 7. While thisdescription is given utilizing as points of reference the top sectionand bottom section, it is understood that these descriptive terms arefor the purpose of reference only and relate only to the normalorientation of the container and are not necessarily limited to aparticular orientation wherein the bottom section is of lower elevationthan the top section.

FIG. 2 of the drawing shows the container 1 in a partially open mode. Itis seen from this view that the container is of a totally unitaryconstruction, being made of but a single section of thermoplasticmaterial with the top section 5, bottom section 3 and hinge portion 7all integrally joined into but a single container. The process ofmanufacturing the case or container, in accordance with this invention,will be given in the remaining description.

A cross section of a blow mold, in accordance with this invention, isillustrated in FIG. 3 of the drawings. Shown in FIG. 3 is a blow mold 9in the open position and comprising mating halves 11 and 13. Suspendedbetween the mating halves 11 and 13 is a parison 14. It is seen thatwhen the mold sections 11 and 13 are in their mated position, theydefine a cavity into which the parison 14 is inflated. While the parison14 is shown as a closed tubular form in FIG. 3, it is understood thatthe initial start-up form would be an open tubular form which would thenbe pinched closed by the closing of the mold sections 11 and 13. Theparison 14 originates from a conventional extrusion source (not shown).

Any blow moldable thermoplastic material having the requisiteflexibility for the hinge may be utilized. Such materials include highdensity polyethylene, polypropylene, polyvinyl chloride and elastomericpolyolefins. The extrusion die may be programmed so as to vary the wallthickness of various portions of the parison so as to minimize anyeffects of sagging. Such techniques are well known in the art.

FIG. 3 illustrates the hinge forming area 15 which may be seen with agreater degree of clarity in FIGS. 5 and 6. FIG. 4 of the drawing showsthe mold sections in the closed position with the parison having beeninflated so as to conform to the geometry of the mold. The inflatedparison is generally designated by the numeral 17. The inflation step iscarried out by the use of needle 19 which communicates with a source ofpressurizing fluid. Such inflation techniques are well known in the art.

The hinge forming area is best seen in FIG. 5 which shows the hingeforming area as a notch or v-shaped portion as indicated at 15. It isseen that, upon inflation of the parison, the parison conforms to wall21 and then into the notched hinge forming area 15. It is understoodthat the thermoplastic material which passes the wall 21 and proceedsinto the notched area 15 will of necessity be of thinner constructionthan the thermoplastic material which rests against wall 21 due to thesection of material conforming to a larger area than that material whichconforms to the vertical wall 21.

In accordance with this invention, it has been found that bysignificantly stretching and deep drawing the thermoplastic materialinto a hinge forming area, the thinning and stretching caused by suchdeep drawing produces a thinned hinge area which is both oriented and ofsignificantly greater flexibility than the adjacent areas. FIG. 5 of thedrawing illustrates a vent 23 which aids the deep drawing of thethermoplastic material by permitting any entrapped gases to escapeduring the deep drawing of the hinge area. The vent 23 may optionally bevacuum assisted so as to further aid in the stretching and deep drawingof the hinge area. FIG. 6 of the drawing shows an enlarged view of thehinge forming area 15 illustrated in FIG. 5. This view is for thepurpose of describing a critical feature of this invention in that thedepth of draw to the suspended length ratio must be greater than 1 inorder to produce an effective hinge. The depth of draw is designated bythe letter "D" in FIG. 6 while the suspended length dimension isdesignated by the letter "S". It is critical that the ratio D/S be atleast 1 or greater. If the ratio D/S is substantially less than 1, thehinge does not possess the required strength or flexibility to functionas a hinge for practical purposes. The parameter D/S is frequentlyreferred to in the art as the draw ratio. The art also frequently refersto the draw ratio being the final area divided by the initial area ofthermoplastic material. If the latter ratio is utilized, the criticaldraw ratio utilizing areas is then √5 for the particular geometryillustrated in the drawings.

Once having inflated the parison to the geometry of the mold includingthe hinge forming area, the resulting closed configuration is severedabout a cicumference contiguous with the hinge portion 7 as shown inFIG. 2. The circumference contiguous with the hinge portion isdesignated by the numeral 25 in FIGS. 1 and 2. The process of severingis carried out by conventional techniques such as placing the containerin a cradle and sawing along a defined path so as to mate the severanceline with the hinge portion 7.

While the hinge forming area 15 of the mold is shown as being ofbasically triangular cross section, it is understood that the shape ofthe hinge may be any desired shape. For example, the hinge forming areamay be rectangular or generally circular in cross section. The onlycritical feature is that the draw ratio (depth of draw to suspendedlength) be 1 or greater.

The container and molds illustrated in the various figures of drawingsillustrate a hinge forming area 15 which is parallel to the direction ofparison drop and on a mold wall adjacent the wall having a parting line.The parting line of the mold shown in FIGS. 4 and 5 is illustrated inFIGS. 1 and 2 by the designation of PL in the dashed line associatedtherewith. The hinge forming area, however, may be on any convenientwall and if on a wall which defines the parting line, the hinge formingarea is preferrably coincidental with the parting line. If the hingeforming area is desired to be on the wall containing the parting lineand does not lie coincidental with the parting line, special moldconstruction is necessitated so as to make it possible to remove themolded article from the mold.

An advantageous feature of the single-walled blow molded container ofthis invention is that either or both the top and bottom sections may beconformed to the geometry of an article which it is intended to house.Such conformity would appear on the interior and the exterior of thecontainer so as to make the geometry of the housed article readilyapparent.

It is thus seen that by this invention a novel single-walled blow moldedcontainer having a deep drawn integral hinge is provided. It is furtherseen that the process of this invention, in conjunction with the uniqueblow mold of this invention, makes it possible to provide such acontainer. As many variations will be apparent to those of skill in theart from a reading of the above specification, which is exemplary innature, the spirit and scope of the present invention is set forth onlyby the breadth of the following appended claims.

What is claimed is:
 1. A blow molding process for forming a parison intoan integral single-walled container comprising top and bottom portionsconnected together by an integral hinge portion, said process comprisingthe steps of:inflating said parison within a hollow mold to conform theparison to the configuration of the interior surface of said mold, saidinterior surface comprising a hinge forming area adapted to create adraw ratio of greater than 1, whereby hinge forming portion of saidparison is simultaneously deep drawn to a draw ratio of greater than 1,thinned and oriented; removing the thus inflated parison from the mold;and severing a circumference of said parison which is contiguous withsaid hinge forming portion to form said container.
 2. The process ofclaim 1 wherein said hinge forming area is generally parallel to adirection of drop of the parison.
 3. The process according to claim 1wherein the hinge forming area is generally perpendicular to a directionof drop of the parison.
 4. The process of claim 1 wherein vacuum meansare utilized to assist in said deep drawing, thinning and orientation ofsaid hinge forming portion.